Method of treating gasoline with citric acid to remove copper



METHOD OF TREATING GASOLINE WITH ClTRIC ACID TO REMOVE COPPER John W.Thompson, Kingsport, Tenm, asslgnor to Eastman Kodak Company, Rochester,N. Y., a corporation of New Jersey No Drawing. Application March 28,1952, Serial No. 279,211

1 Claim. (Cl. 196-39) This invention relates to a method of improvingthe quality of petroleum hydrocarbons, and more particularly, toimproving the quality of petroleum hydrocarbons which have been treatedwith copper-containing reagents for the removal or conversion of sulfurcompounds.

It is well known to remove sulfur compounds, such as mercaptans, frompetroleum hydrocarbons, such as gasoline motor fuels, or to convert suchmercaptans into less objectionable compounds .by appropriate chemicaltreatment, generally referred to as a sweetening operation. One quitecommon method of sweetening involves the use of a doctor solution madefrom sodium hydroxide and lead oxide. Treatment of the sour gasolinewith this solution and .added sulfur converts the mercaptans to alkyldisulfides. The amount of sulfur used must be very carefully controlledsince excess sulfur in the gaso line is harmful with respecttocorrosiveness, lead susceptibility and inhibitor susceptibility. Onthe other hand, the useof insufiicient sulfur causes lead mercap' tidesto be left in'the fuel.

Instead of using the doctor solution method, it has been previouslyproposed to substitute other sweetening operations employing coppersalts for thepurpose of removing the sulfur compounds or converting theminto less objectionable substances. This operation is widely used forthe treatment of petroleum motor fuels, such as gasoline. Frequently inthe copper sweetening process various copper compounds may be carriedover into the treated gasoline where they -are very objectionable sinceeven in trace concentrations they catalyze oxidative deterioriation ofthe treated hydrocarbon. This difficulty is somewhat alleviated throughthe use of the known antioxidants, although the amount of improvement isnot great enough to completely overcome the objections noted above. Itis, therefore, desirable to provide some method which wouldsubstantially completely remove all heavy metal compounds from thepetroleum hydrocarbon, thus allowing the antioxidant to function at itsfullest efficiency.

It is, therefore, an object of my invention to provide an improvedmethod of removing. metals, such as copper, from petroleum hydrocarbons..Another object is to render petroleum hydrocarbons, such as crackedgasoline, more stable to oxidative deterioration catalyzed by metals andto permit more effective use of gasoline antioxidants.

Still another object is to provide a class of new and eifective treatingagents for removing such metals from petroleum hydrocarbons, such ascracked gasoline. Other objects will become apparent from aconsideration of the following description and examples.

According to my invention, I provide the novel effects mentioned aboveby treating a petroleum hydrocarbon which has been sweetened withreagents containing copper with a solution containing certain types ofaliphatic carboxylic acids. The aliphatic carboxylic acids which areuseful in practicing my invention comprise aliphatic hydroxymouocarboxylic acids, such as lactic, glycolic, e-hydroxy isobutyricacids, etc., and aliphatic polycarboxylic acids selected from thoserepresented by the following general formula:

t-gp.-. (-ihtigs wherein R, R1, R2, R3, R4 and R5 each represents amember selected from the group consisting of a hydrogen atom, a hydroxylgroup, a carboxyl group, an alkyl group (e. g. methyl, ethyl, etc.), andan aryl group (e. g.

Advantageously, the petroleum hydrocarbon which has been treated with acopper-containing reagent is washed with an aqueous solution of one ofthe aliphatic carboxylic acids of my invention. The aliphatic'carboxylic acid reacts with the residual copper reagent in the petroleumhydrocarbon and substantially completely removes said copper reagentfrom thetreated hydro-' carbon. Since the reaction product between thecopper reagent and the aliphatic carboxylic acid has a-higher solubilityin the water than it has in the petroleum-hydrocarbon, it is dissolvedinthe, water, thus leaving the petroleum hydrocarbon substantially freeof copper reagent. Efficient mixing between the aqueous solution 7containing the aliphatic carboxylic acid and the pet-roleum' hydrocarbonassures substantially complete re moval of the copper reagent.

The aqueous reagent solution contains one or more of the aliphaticcarboxylic acids and the concentration of acid can be varied accordingto the petroleum hydrocarbon being treated. 0.1 up to the weight percentrequired for a saturated solution of acid in water is effective for thepurposes of my invention.

The process of my invention can be carried out in any suitable manner,such as a batch or continuous type operation, wherein suitable contactof petroleum hydrocarbon and washingsolution can be had. As an exampleof one possible method, the washing solution and petroleum hydrocarbon,such as cracked gasoline, are

intimately mixed-in one chamber and the mixture alor no solubility inthe petroleum hydrocarbon.

lowed to settle either in the same or another vessel.

- After separation into two layers, the upper layer comprising thepetroleum hydrocarbon, now substantially free of metal content, isWithdrawn for further treatment or disposal as required. In someinstances, it may be felt desirable to further Wash the gasoline withwater to remove any other remainingtraces of washing solu-' tion,although tests have shown an after treatment with water to beunnecessary. Apparently, the contrasting left in the petroleumhydrocarbon.

until disposal is indicated by high metal content.

solvent can be employed. When an. organic solvent is desired, it isadvantageously selected so that it is a solvent for the-aliphaticcarboxylic acid but has little It is I thus possibleto effectivelyseparate the organic solvent Patented Mar. 20, 6 j v Generally, asolution of from Instead of using an aqueous solution of the aliphatic,carboxylic acid, a solution of the acid in an organic;

solution containing the aliphatic carboxylic acid from the treatedpetroleum hydrocarbon.

After treatment of the petroleum hydrocarbon with the solutioncontaining the aliphatic carboxylic acid, the treated petroleumhydrocarbon can then be stabilized against oxidative deterioration byaddition of one or more of the known antioxidants ordinarily used forthis purpose. Such antioxidants comprise, for example, thep-aminophenols, hydroquinones, p-phenylenediamines,. etc. See,

Efjecz'iveness of organic acids in washing copper from gasoline SECTIONA Induction Period Before Washing Induction Period After Washing s 1Effective- Sample No. S l Sam 10+ amp e ness,

Samole Sample-iamp 8 r Sernp1e+ p Cu+ percent Blank L Cu+ ll ashmg AgentCu+ Cu BAP BAP Cu BAP 95 55 515 167 water 410 10D 57 525 185 citric aci555 540 100+ 100 67 530 185 d-tartsric acid. 547 537 100+ 95 55' 517 160malonic acid. 547 550 100+ 95 55 515 167 oxalic acid 535 100+ SECTION Bs5 45 512 so. water 55 s5 4 4....-. 95 45 512 60 citric acid l 130 49707 for example, Brimer U. 8. Patent 2,496,930, issued February 7, 1950,von Bramer et a1. U. S. Patent 2,323,948, issued July 13, 1943, etc.

The efficiency of the solution containing, the aliphatic carboxylic acidin removing the heavy metal, such as copper, from the petroleumhydrocarbon, such as cracked gasoline, was determined by means of oxygenbomb stability tests on unwashed and solution-washed samples ofcoppericontaining cracked gasoline, which were inhibited with a gasolineantioxidant just prior to testing. Simultaneously, control tests weremade on the cracked gasoline containing various combinations of copperandantioxidant. In the examples described below, the copper was added inthe form of a benzene solution of copper oleate and the antioxidant usedwas N-n-butyl-p-aminophenol, although other antioxidants were found tobe equally effective for demonstrating the results of my invention. Thewashing consisted of shaking the cracked gasoline with 10 volume percentof a 10 weight percent aqueous aliphatic carboxylic acid solution for 5minutes in a separatory funnel. The treated cracked gasoline was removedand then tested. by means of an oxygen bomb stability test.

In the oxygen bomb stability test, 200 cc. samples of gasoline in glass.bottles were heated at 100 C. in stainless steel bombs. under 100 p. s.i. oxygen pressure. The induction period of the gasoline was measured asthe time in minutes before rapid oxidation of the gasoline began, asevidenced by a sharp drop in oxygen pressure. The following tableillustrates the effect of various solutions of aliphatic carboxylicacids in removing the copper from the cracked gasoline. Insection A ofthe table, an amount of copper oleate was employed suificient to give anequivalent of l.() mg. of copper per liter, while in section B, anamount of copper oleate was employed in an amount sufiicient to give 5.0mg. of copper per liter. The abbreviation BAP stands forN-n-butyl-p-aminophenol. The induction period in minutes is given beforewashing with the aqueous solution containing the aliphatic carboxylicacid, and similar data are given for the cracked gasoline after washing.The eifectiveness in percent of the particular washing agent is given inthe last column, the figure being obtained according to the equation:

(Induction period of) washed gasoline conwashed gasoline containtainmgBAP+Ou ng BAP-k-Cu (Induction period oi) (Induction period of un-)Induction period of 1111-) E11 ectiveness unwashed g as o l l n e washedgasoline containcontaming BAP ing BAI+Ou The purpose of section B in theabove table is to show that while water alone does effectively removesome residual copper sweetening agent when the concentration of theagent is low, as is true in section A, this is by no means the case whenthe concentration of residual copper sweetening agent is higher, suchasmight ordinarily be encountered in the treatment of cracked gasoline, asis true in section B. The citric acid used in arriving at the resultsgiven in the table was employed as the monohydrate. in the above tablewas 0.0048 weight percent. The particular gasolines employed were aPennsylvania cracked gasoline consisting of a blend ofcatalytically-cracked and thermally-cracked fuels.

The above table is believed to clearly show that the aliphaticcarboxylic acids of my invention eifectively reduce the amount of coppersweetening agent in the cracked gasoline to such an extent that theconventional gasoline antioxidants can stabilize the fuel in the desiredmanner. It will be noted, for example, from the table that while sampleNo. 7 gave an effectiveness of 97 percent, i. e-., the treatment withthe solution of citric acid returned the induction period to within 97percent of that obtained when the gasoline was completely free of copperoleate, sample No. 6 gave a corresponding induction period return ofonly 4 percent.

What I claim as my invention and desire secured by Letters Patent of theUnited States is:

A process of stabilizing cracked gasoline which has been sweetened witha copper-containing reagent which comprises intimately mixing saidcracked gasoline with anaqueous solution containing from 0.1 up to theweight percent required for a saturated solution in water of citricacid, and separating said cracked gasoline from said aqueous solutioncontaining the citric acid.

References Cited in the file of this patent UNITED STATES PATENTS Theconcentration of the BAP where indicated

